As the variable valve actuation device, one described in Japanese Laid-Open Patent Publication No. 2009-167989 is known, for example.
The variable valve actuation device is provided with a sensor that determines whether the input rotating body and the output rotating body are fixed to each other. A deviation ratio is calculated, which is a ratio between a deviation amount in a positive direction and a deviation amount in a negative direction of an output signal of the sensor with respect to a reference value. The deviation ratio varies as follows depending upon whether or not the input rotating body and the output rotating body are fixed to each other. That is, when the rotating bodies are fixed to each other, the deviation ratio is not more than a predetermined value. When the rotating bodies are not fixed to each other, since the output rotating body oscillates with respect to the input rotating body, the deviation ratio becomes greater than the predetermined value. According to the variable valve actuation device, in a stoppage process of rotation of the internal combustion engine, it is determined that the rotating bodies are fixed to each other when the deviation ratio is not more than the predetermined value, and it is determined that the rotating bodies are not fixed to each other when the deviation ratio is greater than the predetermined value.